Process in the extrusion of films of thermoplastic material in tubular form and an arrangement for carrying out the process



A nl 9, 1968 s. A. JANSSON ET AL IN THE EXTRUSION OF FILMS OF THERMOPLASTIC MATERIAL IN TUBULAR FORM AND AN ARRANGEMENT FOR CARRYING OUT THE PROCESS PROCESS Filed May 17, 1965 IN VENTORS E n I E on n N .swa R "510 O m H K m? A $3 M n n M 0 TO G nn k m o SIE United States Patent 3,377,413 PROCESS IN THE EXTRUSTON 0F FILMS 0F THERMGPLASTIC MATERIAL IN TUBULAR FORM AND AN ARRANGEMENT FOR CAR- RYING OUT THE PROCESS Sven August Jansson, John Iwan Johansson, and Erik Johan Mariedahl, Upplands Vasby, Sweden, assignors to Aktiebolag'et Svenska Metallverken, Vasteras, Sweden, a joint-stock company limited Filed May 17, 1965, Ser. No. 456,163 Claims priority, application Sweden, May 15, 1964, 59,994/64 9 Claims. (Cl. 264-95) The present invention relates to a process in the extrusion of films of thermoplastic material in a tubular form whereby the tube forced out of the nozzle is subjected to an inner gas pressure and in a thus inflated condition is drawn through one or more cooling liquid columns surrounding the outside of the tube from which columns the cooled tube is permitted to leave during passage through sealing members'which restrict the conveyance of cooling liquid.

When manufacturing films by means of continuous extrusion of thermoplastic material through annular nozzles one has hitherto usually cooled the tubular fihn forced out through the nozzle by means of air. Due to the poor cooling effect of air, cooling often limits the capacity of the machine.

In an attempt to remedy this inconvenience, it has been suggested to improve the cooling action of the air by using, for example cooled air, air having high moisture content, etc. These methods do not enable appreciably improved capacity either. To increase the volume of air or its velocity over certain values, means an impairment of the quality of the product.

Since air cooling has thus shown itself unequal to the high requirements of efiiciency one has in many ways attempted to cool the film against chilled contact surfaces in the form of water cooled heads or matrice, for example. It has thereby been shown that the method can be well carried out as long as said surfaces are clean but due to unavoidable deposits from the extruded material on these, a coating soon appears which causes increased friction and reduced cooling effect.

Further attempts have therefore been made to increase the cooling effect without risk of disturbing or interrupting the operation and attempts have thereby been made to cool the film by permitting the same to come into direct contact with cooling liquid.

According to one of the suggestions developed in this context one has permitted the discharged, still warm and plastic tubular film in inflated condition to pass through a pipe together with running cooling liquid also serving as a lubricant in order to reduce friction between the tubular film and the inner wall of the pipe. It has, however, been shown that distribution of the liquid over the inner wall of the tube has been uneven and that the film therefore has not been smooth. Further, the transparency of the film becomes all too uneven to be accepted.

According to another suggestion an enclosing cascade of cooling liquid is permitted to stream downwards in contact with the outer wall of the film but this step on one hand means that annular liquid-waves strike the film and give it a non-desirable wave-shaped appearance.

These inconveniences are eliminated however by the invention, which is mainly characterized in that the tubular film is drawn through the sealing members past an effective, relatively thin sealing edge under such contact pressure against said edge that the conveyed layer of cooling liquid will be so thin that droplet formation or running 3,377,413 Patented Apr. 9, 1968 of liquid down the walls of the tubular film will be prevented.

The invention also relates to an arrangement for carrying out the process according to the invention, which is mainly characterized in that the effective portion of the sealing members is constituted by a relatively thin, annular sealing edge.

The invention will be more closely described with reference to a diagrammatically shown embodiment of the invention on the attached drawing, and in conjunction therewith further characterizing features of the invention will be disclosed.

FIGURE 1 shows diagrammatically in cross section an arrangement for extrusion of tubular films of thermoplastic material.

FIGURE 2 shows a section of a sealing member according to the invention, cooperating with the passing outer wall of a newly extruded tubular film.

FIGURE 3 shows a similar section of an alternative embodiment of the sealing member according to the invention.

FIGURE 4 shows still another alternative embodiment of the sealing member according to the invention.

With reference to FIGURE 1, an extrusion nozzle is indicated by the reference numeral 1 which nozzle is provided with a delivery channel 2 for a gasfor example airunder a certain overpressure. A tubular film 3 is continuously ejected from the nozzle 1, which film is kept infiated with air injected through the hole or channel 2. The tubular film is allowed to pass through a numberfor example two-vcssels 4 and 5, which are supplied with holes adapted to the current tubular film. The vessels 4 and 5 are provided with annular spill ways 6 and 7 for a cooling liquid 8 which is continuously-in restricted amountsdelivered to the vessels and overflows in a direction towards the tubular film passing through the holes in the bottom of the vessels.

The bottoms in the vessels 4 and 5 present, around said holes, sealing members 9 and 10 characteristic for the invention which consists of a relatively thin, annular sealing edge. These edges can constitute integral sections of the bottom of the vessel proper but are preferably made in the form of separate rings which are placed in and secured, causing a seal around the edge of said hole in the bottom of the vessels.

Cooling liquid is thus supplied to the vessels 4 and 5 through the inlets 11 and 12, respectively, at such a rate that a steady and well adapted amount of cooling liquid streams over the spill ways 6 and 7 and maintains a suitable liquid level 13 in the inner annular portion-restricted by the spill wayof each vessel 4 and 5.

Due to a pre-regulated inflation of the through-going plastic film, said film is caused to abut-with such an adapted pressurethe edge shaped sealing members that the necessary amount of liquid is carried for lubricating the passing tube.

By shaping the sealing members as thin as an edge, firstly very little friction between the edge and the film occurs whereby no chance of wear arises. Further, the seal between the edge and film is so effective that liquid running down the outer sides of the film can be prevented. This enables extrusion to be carried outwithout risk of interruption, at high speeds, and obtain an extraordinarily good quality of the final product.

When the extruded film has passed through the vessels containing cooling liquid, said film has received a stable consistency and can now be carried away continuously for spooling, storing or the like. The tube is therewith allowed to pass between two angularly positioned, preferably porous or open-work guide surfaces 14 and 15 which converge towards two clamping rolls or the like indicated by 16 and 17, between which the film is clamped or folded into one outgoing double web 18 which, subsequent to the removal of possibly remaining cooling liquid, is spooled or used in some other way, or stored. In this context it may even be mentioned that both clamping rolls also contribute towards clamping the tube together so that air does not leak out of the tube. A drip tray or the like 19 is arranged under the entire arrangement, for receiving the overflowing cooling liquid from the vessels 4 and 5.

According to the invention, the sealing members 9 and 10 can be constituted of rigid sealing edges. According to a preferred embodiment of the invention these edges are suitably made of elastic, resilient material, such as rubber, plastic or the like.

Further, according to the invention it is advantageous to shape the sealing members so that theyin a more advantageous manner-accommodate the passing plastic film. It is thus shown in FIGURE 2 the manner in which the edge 9 is curved so that only a substantially linear restrictingring exists through which the plastic film passes. The member 9 shown in FIGURE 2 can either be curved beforehand to the form shown, i.e. be a relatively rigid member, or alternatively if this sealing member is made of an elastic resilient material said member during the operation proper can be curved downwards and retained curved in the position shown whilst carrying out its function.

A further example of a sealing member 9 is shown in FIGURE 3 which member can also be either of a rigid or elastic resilient material whereby this section also produces a substantially linear restricting ring to the film.

FIGURE 4 shows a further modified embodiment of a sealing member according to the invention, which member consists of a flat continued plate which is caused to taper along a curve in the moving direction of the film at 20. This member 9 can also be made of rigid metallic material or alternatively of resilient material such as rubber, plastic or the like. Other embodiments with the view of increasing or reducing conveyance of cooling liquid can also exist.

The cooling effect according to the above disclosed method can be further prompted by adding special wetting agents to the cooling liquid.

In certain cases it can be advantageous to add viscosity raising elements to the cooling liquid.

The surface tension and viscosity of the cooling liquid can be regulated using one or both of these manufacturing methods in such a way that when using edge shaped sealing members according to the invention the wetting degree of the film becomes the one most suitable for each manufacturing purpose. The cooling liquid moreover can be given such composition that it gives the manufactured film required properties in respect to for example adhesiveness or capability of being printed upon or in order to prevent the film becoming charged with static electricity.

The invention is not limited to the shown or described embodiment of the same but can be varied in many ways within the scope of the accompanying claims.

What is claimed is:

1. In the extrusion of films of thermoplastic material in tubular form, in which the tube is forced out of a nozzle, and is subjected to an inner gas pressure, a method of cooling the tube comprising the steps of drawing the tube through at least one body of cooling liquid, and then drawing the tube from said liquid while applying a constant thin edge pressure contact around the circumference of said tube to maintain a thin layer of liquid on the surface of the tube to lubricate same, and to prevent the formation of droplets on, and the running of liquid down, the surface of said tube.

2. A process according to claim 1, further comprising the step of adding a wetting agent to the cooling liquid.

3. A process according to claim. 1, further comprising the step of adding a viscosity raising element to the cooling liquid.

4. A process according to claim 1, further comprising the step of adding elements to the cooling liquid which influence the ability of the produced film to be printed upon and also its adhesive power.

5. In the extrusion of films of thermoplastic material in tubular form, in which the tube is forced out of a nozzle, and is subjected to an inner gas pressure, an ap paratus for cooling the tube, said apparatus comprising at least one annular vessel containing cooling liquid, means to draw said tube from said nozzle through said vessel so that the liquid surrounds the outside of said tube, and a sealing member extending from said vessel in the path of said tube after it leaves said'vessel, said sealing member having'a relatively thin annular edge in contact with said tube in order to maintain a thin layer of liquid on the surface of the tube to lubricate same while applying constant pressure against said tube to prevent the formation of droplets on, and the running of liquid down, the surface of said tube.

6. The apparatus of claim 5, wherein said vessel includes at least one annular spillway for said cooling liquid.

7. The apparatus of claim 5, in which the edge of said sealing member is rigid.

8. The apparatus of claim 5, wherein the edge of said sealing member is elastic.

9. The apparatus of claim 5, wherein said sealing member is in the form of a metal disk.

References Cited UNITED STATES PATENTS 2,955,321 10/ 1960 Fortner et al. 264-95 3,142,092 7/1964 Ralston 264-95 3,169,272 2/1965 Maxson 18-14 FOREIGN PATENTS 664,048 5/ 1963 Canada. 1,286,920 1/ 1962 France.

8,16 9 10/1962 Great Britain.

ROBERT F. WHITE, Primary Examiner.

A. R. NOE, Assistant Examiner. 

1. IN THE EXTRUSION OF FILMS OF THERMOPLASTIC MATERIAL IN TUBULAR FORM, IN WHICH THE TUBE IS FORCED OUT OF A NOZZLE, AND IS SUBJECTED TO AN INNER GAS PRESSURE, A METHOD OF COOLING THE TUBE COMPRISING THE STEPS OF DRAQING THE TUBE THROUGH AT LEAST ONE BODY OF COOLING LIQUID, AND THEN DRAWING THE TUBE FROM SAID LIQUID WHILE APPLYING A CONSTANT THIN EDGE PRESSURE CONTACT AROUND THE CIRCUMFERENCE OF SAID TUBE TO MAINTAIN A THIN LAYER OF LIQUID ON THE SURFACE OF THE TUBE TO LUBRICATE SAME, AND TO PREVENT THE FORMATION OF DROPLETS ON, AND THE RUNNING OF LIQUID DOWN, THE SURFACE OF SAID TUBE. 